1) Field of the Invention
The present invention relates to a fabrication method for a photomask, a fabrication method for a device and a monitoring method for a photomask suitable for use for formation of a fine pattern when various solid-state devices such as, for example, a semiconductor device, a magnetic device element and so forth are fabricated.
2) Description of the Related Art
In recent years, it is demanded to form a very fine pattern in fabrication of an LSI (Large Scale Integrated circuit).
To this end, at an exposure step of transferring a fine circuit pattern to a wafer (semiconductor substrate), a photomask (phase shift mask) having a function for changing the phase of light used for light exposure to raise the contrast is used. Particularly, from such reasons as easy fabrication, a halftone type phase shift mask is used popularly.
The halftone type phase shift mask is formed, for example, as shown in FIG. 7(F), by laminating a translucent halftone phase shift layer 2 and a shading layer 3 in order on a transparent substrate 1 such as a synthetic quartz substrate.
The halftone type phase shift mask includes, for example, as shown in FIG. 6, a circuit pattern region (mask pattern region) 8 on which a circuit pattern (main pattern) to be transferred to a semiconductor chip is formed. In the circuit pattern region 8, the circuit pattern is formed by removing the shading layer 3 and removing the halftone phase shift layer 2 in accordance with the circuit pattern to expose the transparent substrate 1.
Where the exposure is performed using the halftone type phase shift mask formed in such a manner as described above, in a region wherein the transparent substrate 1 is exposed, light from an illumination system transmits as it is. On the other hand, in another region wherein the halftone phase shift layer 2 is exposed, the light from the illumination system transmits with the phase thereof shifted by 180 degree.
Meanwhile, the shading layer 3 remains in a region of the halftone type phase shift mask outside the circuit pattern region 8. Consequently, when the circuit pattern is transferred to the wafer, multiple exposure in an adjacent circuit pattern region (not shown) is prevented.
It is to be noted that, in FIG. 6, reference numeral 81 denotes a barcode pattern for mask identification, 82 a numbering pattern for mask identification, and 83 a fiducial pattern for positioning with a light exposure apparatus.
Incidentally, in such a photomask as described above, the assurance and management of the accuracy of the mask pattern are significant. As the accuracy assurance method for photomasks, an assurance method of the position accuracy and an assurance method of the dimensional accuracy are available.
Thus, assurance and management of the accuracy is conventionally performed by laying out monitor patterns on the inside and outside of an effective transfer region as occasion demands and measuring the monitor patterns. It is to be noted that a pattern forming method is disclosed, for example, in Japanese Patent Laid-Open No. 2002-107911.
Preferably, from a point of view that the accuracy of a photomask is measured with accuracy, as monitor patterns, simple diagrammatic patterns suitable for assurance and management of the accuracy are disposed at appropriate locations.
In the halftone type phase shift mask described above, as shown in FIG. 6, monitor patterns 6A for positional accuracy assurance of the mask pattern and monitor patterns 6B for dimensional accuracy assurance of the mask pattern are formed as the mask patterns 6 in a region outside a desired effective transfer region (in FIG. 6, a region which is surrounded by a broken line) 7 which includes the circuit pattern region 8.
Such a halftone type phase shift mask including the monitor patterns 6 (6A and 6B) as described above is fabricated in the following manner.
First, as shown in FIG. 7(A), a halftone phase shift layer 2 and a shading layer 3 are laminated on a transparent substrate 1.
Then, as shown in FIG. 7(A), a first resist layer 4 is formed on the shading layer 3, and, as shown in FIG. 7(B), a circuit pattern 5 and monitor patterns 6 (monitor patterns 6A for positional accuracy assurance and monitor patterns 6B for dimensional accuracy assurance) as a first resist pattern 4p are formed by performing processes including exposure (drawing), PEB (Post Exposure Bake) and development for the first resist layer 4.
Then, as shown in FIG. 7(C), the shading layer 3 is etched while the first resist layer 4 having the first resist pattern 4p thereon is used as a mask to form the circuit pattern 5 and the monitor patterns 6 (monitor patterns 6A for positional accuracy assurance and monitor patterns 6B for dimensional accuracy assurance) as the shading pattern 3p on the shading layer 3. Thereafter, the first resist layer 4 is removed.
Then, as shown in FIG. 7(D), the halftone phase shift layer 2 is etched while the shading layer 3 on which the shading pattern 3p is formed is used as the mask to form the circuit pattern 5 and the monitor patterns 6 on the halftone phase shift layer 2.
Thereafter, as shown in FIG. 7(E), a second resist layer 4A is formed on the shading layer 3, and a second resist pattern 4Ap for forming a desired effective transfer region (scanning region) 7 (refer to FIG. 6) including a circuit pattern region 8 (refer to FIG. 6) is formed by performing processes including exposure (drawing), PEB and development for the second resist Layer 4A. Then, as shown in FIG. 7(F), the shading layer 3 is selectively etched while the second resist layer 4A having the second resist pattern 4Ap thereon is used as the mask. Thereafter, the second resist layer 4A is removed. Consequently, the halftone type phase shift mask (photomask) is completed.
Then, the monitor patterns 6 (monitor patterns 6A for positional accuracy assurance and monitor patterns 6B for dimensional accuracy assurance) are measured in a state wherein the halftone type phase shift mask is completed.
In this manner, where the halftone type phase shift mask is fabricated, measurement of the monitor patterns 6 is performed and assurance and management of the accuracy of the mask pattern is performed in a state wherein the halftone type phase shift mask is completed.